1. Field of the Invention
The present invention relates to a pump and more particularly to an improvement in an auxiliary radially shifting mechanism for vanes in a pump of the vane type.
2. Description of the Prior Art
Hitherto, the pumps of this type have generally had a constitution such as that illustrated in FIGS. 1, 2, and 3 of the attached drawings in which a rotor 5, fixedly secured to a driving shaft 1, is rotatably received within a cup-shaped cylinder 2, said rotor 5 being eccentric to the center of the cylinder. A number of vanes 7 is disposed within slots 5a formed in rotor 5 so as to be radially shiftable, and these vanes 7 are adapted to have their radial outer ends abut against the inner periphery of cylinder 2 so that fluid is sucked through a suction port 8 provided in cylinder 2 to be discharged throgh a discharge port 9 also provided in cylinder 2. In the drawings, the reference numeral 3 is a bracket secured to cylinder 2 to sealingly close cylinder 2; 4 is a bearing to rotatably support driving shaft 1 in bracket 3; 6 is a fluid seal to prevent the fluid within cylinder 2 from leaking; and 3a is a ring-shaped projection provided on bracket 3 so as to be concentric with cylinder 2.
The operation of the pump described above is as follows.
As rotor 5 is rotated by means of driving shaft 1 by a prime mover (not shown), centrifugal force is applied to vanes 7 radially shiftably disposed within slots 5a formed in rotor 5 so that they are urged radially outwards in slots 5a, vanes 7 revolving relative to cylinder 2 with their radially outward end portions abutting against the inner periphery of cylinder 2. Due to the constitution as above described, as vanes 7 revolve, the fluid enclosed within fluid delivery chambers 2a and 2b each defined by the inner periphery of cylinder 2, rotor 5 and neighboring vanes 7 is discharged through discharge port 9, new fluid being again sucked through suction port 8, and thus the pump functions as a fluid pump to deliver the fluid under pressure. In this conventional pump, ring-shaped projection 3a provided on bracket 3 and being concentric with cylinder 2 acts such that, when the centrifugal force applied to vanes 7 is low as a result of a low rotary speed of rotor 5, it forcefully thrusts vanes 7 radially outwards with respect to rotor 5 so as to cause the radially outward ends of vanes 7 to abut against the inner periphery of cylinder 2 so as to form fluid delivery chambers 2a and 2b.
From the foregoing it will be appreciated that the conventional pump of the vane type having the constitution and the operation as above described exhibits such defects that, at the time of a low rotational speed of rotor 5, since the centrifugal force to be applied to vanes 7 is low, when the fluid pressure at the side of suction port 8 varies, the varied fluid pressure acts as a force to urge vanes 7 downwards, causing vane 7 to exhibit a hunting phenomenon i.e. oscillating up and down in an effort to find an equilibrium position, thus causing incomplete closure of fluid delivery chambers between the inner periphery of cylinder 2 and the outer periphery of ring-shaped projection 3a, as the result of which vanes 7 impinging upon the outer periphery of ring-shaped projection 3a are partially subjected to abnormal wear. Incidentally this hunting phenomenon or oscillation is remarkably experienced in the range over 180.degree. after completion of the raising of the vanes 7.